One of the most timely problems with leather production is the partial or complete replacement to be found for auxiliary agents, which put a high load on industrial sewage waters. This is the case particularly with the defatting and pretanning of pickled hides and the tanning of pelts and leather. Thereby aside from tanning matter other auxiliary agents, such as solvent and defatting agents, tensides, electrolytes, phosphates, neutralizers, etc. are utilized.